Disc brake with integral parking brake

ABSTRACT

A disc brake caliper assembly includes a hydraulically actuated first piston, a second piston engagable with the first piston, a mechanical actuating mechanism which moves axially into the housing when actuated, and an extendable member acting between the adjuster piston and the mechanical actuating mechanism and including an apertured locking plate closely surrounding a shaft to form a one-way clutch. The extendable member provides a rigid force transmitting linkage between the mechanical actuating mechanism and the pistons for mechanical actuation of the brake. An adjuster spring increases the length of the extendable member to move the adjuster piston into closer relationship with the disc to adjust for lining wear.

United States Patent 1 [111 3,724,605

Naismith et al. 11 Apr. 3, 1973 541 DISC BRAKE WITH INTEGRAL 3,605,9599/1971 Beck ..188/7l.8 x

PARKING BRAKE [75] Inventors: vThomas D. Naismith, Dayton; PnmaryExaminer-4' Henson wood Ronald L. Shellhause, Vandalia,

both of Ohio [73] Assignee: General Motors Corporation,

Detroit, Mich.

[22] Filed: Nov. 3, 1971 [21] Appl. No.: 195,285

[52] U.S. CI. ..l88/71.8, 188/196 P [51] Int. Cl ..Fl6d 65/54 [58] Fieldof Search ..l88/7l.7, 71.8, 196 P ['56] References Cited UNITED STATESPATENTS 2,951,560 9/1960 Smellie................................188/71.8 3,589,478 6/1971 Plaat et al.............l88/7l.8 X 3,589,479 6/1971 Plaat et al ..188/7l.8 X

26 N r w J 1/ f u m 1.2

Assistant Examiner-Michael Mar Attorney-JV. E. Finken et al.

[57] ABSTRACT A disc brake caliper assembly includes a hydraulicallyactuated first piston, a second piston engagable with the first piston,a mechanical actuating mechanism which moves axially into the housingwhen actuated, and an extendable member acting between the adjusterpiston and the mechanical actuating mechanism and including an aperturedlocking plate closely surrounding a shaft to form a one-way clutch. Theextendable member provides a rigid force transmitting linkage betweenthe mechanical actuating mechanism and the pistons for mechanicalactuation of the brake. An adjuster spring increases the length of theextendable member to move the adjuster piston into closer relationshipwith the disc to adjust for lining wear.

5 Claims, 2 Drawing Figures 3 as 62 86 5o PATENTEDAPRS m5 3.724.605

I r I ,9 14 Z 2 I N VEN TORS ATTORNEY DISCBRAKE WITH INTEGRAL PARKINGBRAKE The invention relates to an improved disc brake assembly and moreparticularly to a disc brake caliper assembly which provides hydraulicactuation for service braking, mechanical actuation for parking brakingand automatic adjustment for lining wear.

It is desirable in an automotive disc brake caliper assembly to providehydraulic actuation of the brakes for service braking and mechanicalactuation of the brakes for emergency or parking braking. It is alsodesirable to provide an automatic wear adjusting mechanism.

The disc brake caliper assembly of this invention includes a firstpiston slidable within the caliper housing and hydraulically actuable toforce brake pad assemblies against the disc. A second or adjuster pistonis also sealingly slidable in the housing and is engageable with thefirst piston to limit retraction thereof. A mechanical actuatingmechanism is provided which moves axially into the housing toward thedisc when actuated. An extendable member including a shaft engaging theadjuster piston and an apertured locking plate closely surrounding theshaft acts between the adjuster piston and the mechanical actuatingmechanism. The mechanical actuating mechanism is engageable with theapertured locking plate alonga limited circumferential portion thereofand a spring acts between the shaft and the locking plate to cock thelocking plate into frictional locking engagement of the shaft. Theextendable member provides a rigid force transmitting linkage betweenthe mechanical actuating mechanism and the pistons for mechanicalactuation of the brake. The adjuster spring increases the length of theextendable member to move the adjuster piston into closer relationshipwith the disc and renewed contact with the first piston whenever liningwear is encountered so as to minimize the extent of actuation on themechanical actuating means necessary for a subsequent mechanicalactuation. A release cup provided within the mechanical actuatingmechanism and surrounding the shaft of the extendable member can beforced against the apertured locking plate to release the locking platefrom frictional engagement of the shaft so that the extendable membercan be collapsed to facilitate replacement of the brake linings. In asecond embodiment of the invention a limited amount of lash or play ispro vided in the mechanical actuating mechanism to permit limitedretraction of the piston and extendable member into the housing tocompensate for brake lining swell.

One feature of the invention is the provision of a disc brake caliperhaving an integral mechanical actuating mechanism with automatic wearadjustment.

Another feature of the invention is the provision of automatic adjustingmechanism which functions to compensate for even the smallest incrementsof lining wear.

The invention also features a device for collapsing the wear adjustingextendable member without extensive disassembly of the caliper tofacilitate a brake lining replacement.

A further feature of the invention is the provision of a disc brakecaliper having an integral mechanical actuating and wearadjustingmechanism whichaccommodates lining expansion.

Another feature-of the invention is awear adjusting mechanism whichadjusts for wear only when the brake is released so thatcaliperdeflection will not be compensated for.

These and other features of the invention will become apparent uponconsideration of the following specification and the drawings in which:

FIG. 1 is a cross sectional view of a caliper assembly embodying theinvention; and

FIG. 2 is a fragmentary cross section view of a disc brake caliperassembly embodying a second form of the invention.

Referring to FIG. 1, the disc brake assembly includes a rotatable disc10 which is attached to the vehicle wheel assembly and a caliperassembly 12. Inner and outer brake shoe assemblies 14 and 16respectively include backing plates 18 and 20 to which are securedsuitable brake linings 22 and 24.

Shoe assemblies 14 and 16 are respectively positioned in the caliperassembly 12 on opposite sides of the disc 10. Piston 26 is slidable inan axially extending bore 28 formed in the caliper housing 30 and formstherewith a fluid chamber 32. Inlet port 34 communicates fluid pressurefrom a master cylinder, not shown, to the fluid chamber 32. Piston 26engages the brake shoe assembly 14 so that when chamber 32 ispressurized piston 26 moves in the caliper housing 30 in the directiontoward disc 10 forcing the shoe assembly into braking engagement withthe disc 10 while the reaction force transferred to the caliper housing30 forces the brake shoe assembly 16 into engagement with the other sideof the disc 10. The hydraulic force is typically of such a magnitude asto result in deflection of that portion of the caliper housing 30 whichbridges the periphery of the disc 10. When hydraulic pressure isrelieved from the hydraulic chamber 32, the piston '26 is retracted intocaliper housing 30 as the caliper deflecting force is relieved. Apressure seal 36-located between caliper housing 30 and piston 26provides sufficient resistance to retracting movement of piston 26 tohold the brake linings 22 and 24 in contact with disc 10 upon brakerelease.

' An extendable wear adjusting mechanism which limits retractingmovement of the piston 26 into the housing 30 and a mechanical mechanismfor actuating the brake is also provided. A rotatable member 40 extendsthrough a bore 42 in caliper housing 30. A lever 44 is attached to theouter end of rotatable member 40 and is connected to the emergency andparking brake control mechanism, not shown. The portion of rotatablemember 40 inside the caliper housing 30 is provided with a number ofcircumferentially spaced axially extending grooves 46. A sleeve 48 islocated in caliper housing 30 and surrounds the rotatable member 40. Aseries of axially extending grooves 50 are formed onthe inner peripheryof sleeve 48 and. are aligned with the grooves 46 of rotatable member40. A number of bearing balls 52 are located in the grooves providing alow friction axial spline connection between the rotatable member 40 andthe sleeve 48. A helical groove 54 is formed on the outer periphery ofsleeve 48 and a mat ing helical groove 56 is formed on an insert 58which threadedly engages the housing 30. A number of bearing balls 60are located in the helical grooves 54 and 56 providing a helical splineconnection between the housing 30 and the sleeve 48 so that whenrotatable member 40 and the sleeve 48 splined thereto are rotated thesleeve 48 moves axially within the housing 30.

An adjuster piston 62 is sealingly slidable on the sleeve member 48 andis engageable with the first piston 26. A shaft 64 is located withinsleeve 48 and piston 62 and is engageable with piston 62 through theintermediary of thrust ball 66. A locking plate or disc 68 is aperturedto closely surround the shaft 64. A cam wedge 74 is seated on a shoulder76 of the sleeve 48. A preloaded spring 70 surrounds shaft 64, and actsbetween a shoulder 72 of shaft 64 and the locking plate 68, therebyurging locking plate 68 into engagement of the cam wedge 74 and holdingadjuster piston 62 in engagement with piston 26. The cam wedge 74engages the locking plate 68 along a minor circumferential portionthereof so that the spring 70 cocks the locking plate 68 into frictionallocking engagement with the shaft 64, thereby forming a one-way clutchwhich prevents shaft 64 from moving relative sleeve 48 in the directionaway from disc but permits its movement toward disc 10. Thus, it may beseen that the retracting movement of first piston 26 is limited by itsengagement with second piston 62 since the shaft 64 cannot be moved inthe retracting direction.

Mechanical actuation of the brake is initiated by rotation of lever44and the rotatable member 40 connected thereto. Rotation of rotatablemember 40 imparts rotary movement to sleeve 48 through the action ofballs 52 in grooves 46 and 50, and results in axial movement of sleeve48 toward the disc 10 by virtue of .the balls 60 riding in helicalgrooves 54 and 56. The axial movement of sleeve 48 is transmittedthroughcam wedge 74, locking plate 68, shaft 64, thrust ball 66, adjusterpiston 62, and first piston 26 to the brake pad assembly 14 causing thebrake pads to be forced against the disc. Return of lever 44 to itsinitial rest position permits the aforel isted parts to return to theirinitial positions to release the brake. If brake linings 22 and 24 haveworn during the mechanical actuation, the pistons 26 and 62 will not bereturned to their premechanical actuation positions within caliperhousing 30. In this event, sleeve 48 and cam wedge 74 return to theirpositions in the housing and spring 70 holds second piston 62 againstfirst piston 26 while causing the locking plate 68 to frictionallydisengage and move along shaft 64 to maintain its engagement with camwedge 74. Subsequent to this adjusting movement, piston 26 cannot beknocked back into the caliper since the locking plate 68 will have onceagain frictionally engaged the shaft 64.

During hydraulic actuation ofthe brake the piston 26 is displaced out ofcaliper housing 30 and away from adjuster piston 62. A seal 86 locatedbetween insert 58 and sleeve 48 and a seal 88 located between sleeve 48and piston 62 prevent the pressure in fluid chamber 32 from acting on heinner portion of piston 62 so that the net hydraulic force acting onpiston 62 in the retracting direction prevents the adjuster spring 70from adjusting the piston 62- toward disc 10 when the brake is beinghydraulically applied; This prevents caliper deflection from resultingin false adjustment. If lining wear occurs during such hydraulicactuation, the first piston 26 will not return to its preactuationposition engaging adsequent to this wear adjusting movement of adjusterpiston 62, first piston 26 cannot be knocked further back into thecaliper since the lockingplate 68 once again frictionally engages theshaft 64. It should be noted that since the adjusting mechanism dependson the movement of apertured locking plate 68 on the smooth surface ofshaft 64, the adjusting mechanism can function to correct even thesmallest increment of lining wear.

In order to permit replacement of the inner and outer brake shoeassemblies 14 and 16, provision is made to release the wear adjustingmechanism. A release cup surrounds the end of shaft 64 and is normallyseated against rotatable member 40. A passage 82 is provided through therotatable member 40 so that a rod may be inserted through rotatablemember 40 into engagement with release cup 80. The rod may then beutilized to push release cup 80 toward the disc whereby it engageslocking plate 68 at a point diametrically opposite the wedge 74 so thatthe locking plate is urged out of frictional engagement with the shaft64. The piston 26 may then be fully retracted into the caliper housing30 to load capacity for the mechanical actuating function of theextendable member. In the embodiment of FIG. 2,

the cam wedge 74 of FIG. I has been eliminated by making the aperturesthrough the, locking plates 98 and 100 at an angle to the axis of thelocking plates so that locking plate l00 directly engages sleeve 48. Inthis case, the release cup 80 hasa beveled end so that it may engage thelocking plate 100 at a point diametrically opposite its point ofengagement with the sleeve 48 to collapse the extendable member, therebyfacilitating lining replacement.

The embodiment of FIG. 2 also allows the rear adjusting mechanism tocompensate for lining expansion due to heat generated by braking. Thiscompensation is provided by lash or play in the helical splineconnection between insert 58 and sleeve 48. This lash is built into Ithe helical spline connection by providing a helical groove 56 formed inthe insert which is of width inexcessof the width of bearing ball 60engaged therein. A Bellville spring 102 acts between the caliperhousing'30 and the end of sleeve 48 to urge sleeve 48 toward the disc10. When the brake linings expand into forced en gagement with the disc10 when the brakes are not actuated, the reaction force transferred tocaliper 3 0 and piston 26 can compress Bellville'spring 102 permitting vthe piston 26 to retract into caliper housing 30 torelieve the brakeengaging force resulting from the expansion. The degree to which suchexpansion may be compensated for is a factor of the amount of lashprovided and the spring rate of Bellville spring 102. It is noted thatthe capacity of Bellville spring 102 must exceed that of the adjusterspring 70 to prevent the adjuster spring 70 from collapsing Bellvillespring 102 and moving sleeve 48 through the compensating lash betweenthe ball 60 and groove 56.

What is claimed is: l. A disc brake assembly having a disc and a brakeshoe assembly and comprising:

a housing including means associated therewith and movable axiallytherein; 5 first piston means in the housing engaging the brake padassembly and forming with the housing a fluid into the housing. 3. Adisc brake assembly having a disc, a caliper housing, and a brake shoeassembly and comprising:

first piston means in the housing engaging the brake pad assembly andforming with the housing a fluid chamber;

pressure has permitted retraction of the first piston chamber; meanscommunicating fluid pressure to the fluid means communicating fluidpressure to the fluid chamber to selectively displace the piston towardchamber to selectively displace the Pi toward 10 the disc to actuate thebrake and permit retraction the disc to actuate h brake and permitretraction of the piston into the housing to release the brake; of thePiston the housing to release the brake; adjuster piston means in thehousing and engageable adjuster piston means in the housing engageablewith ith the first piston;

the first piston to retraction thereof; 5 shaft means engaging the econdpiston;

extehdeble force hehsmhtihg means extending 1 apertured locking platemeans closely surrounding between the associated means and the adjusterthe h ft means; Plstoh Theehs e lhehldihg, h" meehs engaging springmeans acting between the shaft means and the one of the piston means andassociated means, p t dl ki g plate means; apertured locking plate meansclosely surrounding means associated with the housing and mcvable shaftshaft means and ehghged by the other of the therein when actuated, theassociated means en- P' f mhahs and ahsoclateh means at f a gaging theapertured locking plate means at only a hmlted clfcumferehhal homothereof Spnhg limited circumferential portion thereof whereby meansacting between the shaft means a the the apertured locking plate meansis cocked into lockmg plate means urgmg exterhslon of frictionalengagement with the shaft so that upon tendable h 'h the :adluster mstonm axial movement of the associated means the closer wear ad ustingrelationship to the disc and locking plate means Shaft means, theadjuster q h the apertured qckmg plate means mm piston means and thefirst piston are forced toward frictional engagement with the shaftmeans so that the disc to actuate the brake,

r ih T r associate; a the housing and the means associated therewithhav- Q 1 g p a e 8 a means e a Jus er ing limited axialrelative movementtherebetween Piston and the first piston are forced toward theindependently of said movement when actuated- CllSC to actuate thebrake. d d b h 3 2 A disc brake assembly having a disc a caliper anSecon spring means actmg etween the ousmg, and the associated means tohold the associated housing, and a brake shoe assembly and comprlsmg: 5

t h h th b k means toward the (118C and yielding to permit the 11stpiston means in t e ousmg engaging e ra e limited m v m m f th t d adassembl and formin with the housin afluid o e e o e assocla 6 means awayEhamber y g g from the disc when the brake pad assembly exmeanscommunicating fluid pressure to the fluid 4 fiz z h g i fi f g z chamberto selectively displace the piston toward 40 e m e o 6 mm at compnsmgmovable means within the housing engageable with the locking plate meansdiametrically opposite its point of engagement with the associatedmeans;

the disc to actuate the brake and permit retraction of the piston intothe housing to release the brake;

adjuster piston means in the housing and engageable with the firstpiston to'limit retraction thereof;

and an axially extending passage through the associated means permittinginsertion of a tool to shaft means engaging the adjuster piston means;

apertured locking plate means closely surrounding fhrclhly urge movablemeahs engagement the h ft means; with the locking plate means to cockthe locking spring means acting between the shaft means and the Platemeehs out 0f frictional ehgegemeht 0f the apertured locking plate means;shaft whereby the shaft means, second piston means associated with thehousing and movable aximeans, and first Pi means y be ally therein, theassociated means engaging the apertured locking plate means at only alimited circumferential portion thereof whereby the spring means cocksthe apertured locking plate means retracted into the housing. 7 5. Thedisc brake of claim 2 wherein the means associated with the housingcomprises;

a rotatable member received through the wall of the into frictionalengagement with the shaft so that housing and i g i u fer'entiallySpaced axiupon axial movement of the associated means the allyBXteflding grooves formed on the periphery of locking plate means, theshaft means, the adjuster the Portion thereof Within the housing; pistonmeans and the first piston are forced toward Sleeve means thin thehousing having circumthe disc to actuate the brake; ferentially spa'cedaxially extending grooves and seal means associated with the adjusterpiston formed on the peripheral portion thereof surmeans in a manner toprovide upon hydraulic acrounding the grooved portion of the rotatabletuation a force acting on the adjuster piston means member and having onthe outer periphery thereof in the retracting direction whereby thespring a helical groove;

means may move the apertured locking plate a helical groove formed onthe housing and mating means on the shaft means to position and hold thesecond piston means in closer wear adjusting relationship to the disconly when the fluid chamber the helical groove of the sleeve; bearingballs located in the respective grooves whereby upon rotation of therotatable member the bearing balls impart ro tary and consequent axialmovement to the sleeve.

1. A disc brake assembly having a disc and a brake shoe assembly andcomprising: a housing including means associated therewith and movableaxially therein; first piston means in the housing engaging the brakepad assembly and forming with the housing a fluid chamber; meanscommunicating fluid pressure to the fluid chamber to selectivelydisplace the piston toward the disc to actuate the brake and permitretraction of the piston into the housing to release the brake; adjusterpiston means in the housing engageable with the first piston to limitretraction thereof; extendable force transmitting means extendingbetween the associated means and the adjuster piston means andincluding, shaft means engaging one of the piston means and associatedmeans, apertured locking plate means closely surrounding shaft shaftmeans and engaged by the other of the piston means and associated meansat only a limited circumferential portion thereof, spring means acTingbetween the shaft means and the locking plate means urging extension ofthe extendable member to move the adjuster piston in closer wearadjusting relationship to the disc and cocking the apertured lockingplate means into frictional engagement with the shaft means so that uponaxial movement of the associated means the locking plate means, shaftmeans, the adjuster piston and the first piston are forced toward thedisc to actuate the brake.
 2. A disc brake assembly having a disc, acaliper housing, and a brake shoe assembly and comprising: first pistonmeans in the housing engaging the brake pad assembly and forming withthe housing a fluid chamber; means communicating fluid pressure to thefluid chamber to selectively displace the piston toward the disc toactuate the brake and permit retraction of the piston into the housingto release the brake; adjuster piston means in the housing andengageable with the first piston to limit retraction thereof; shaftmeans engaging the adjuster piston means; apertured locking plate meansclosely surrounding the shaft means; spring means acting between theshaft means and the apertured locking plate means; means associated withthe housing and movable axially therein, the associated means engagingthe apertured locking plate means at only a limited circumferentialportion thereof whereby the spring means cocks the apertured lockingplate means into frictional engagement with the shaft so that upon axialmovement of the associated means the locking plate means, the shaftmeans, the adjuster piston means and the first piston are forced towardthe disc to actuate the brake; and seal means associated with theadjuster piston means in a manner to provide upon hydraulic actuation aforce acting on the adjuster piston means in the retracting directionwhereby the spring means may move the apertured locking plate means onthe shaft means to position and hold the second piston means in closerwear adjusting relationship to the disc only when the fluid chamberpressure has permitted retraction of the first piston into the housing.3. A disc brake assembly having a disc, a caliper housing, and a brakeshoe assembly and comprising: first piston means in the housing engagingthe brake pad assembly and forming with the housing a fluid chamber;means communicating fluid pressure to the fluid chamber to selectivelydisplace the piston toward the disc to actuate the brake and permitretraction of the piston into the housing to release the brake; adjusterpiston means in the housing and engageable with the first piston; shaftmeans engaging the second piston; apertured locking plate means closelysurrounding the shaft means; spring means acting between the shaft meansand the apertured locking plate means; means associated with the housingand movable therein when actuated, the associated means engaging theapertured locking plate means at only a limited circumferential portionthereof whereby the apertured locking plate means is cocked intofrictional engagement with the shaft so that upon axial movement of theassociated means the locking plate means, shaft means, the adjusterpiston means and the first piston are forced toward the disc to actuatethe brake; the housing and the means associated therewith having limitedaxial relative movement therebetween independently of said movement whenactuated; and second spring means acting between the housing and theassociated means to hold the associated means toward the disc andyielding to permit the limited movement of the associated means awayfrom the disc when the brake pad assembly expands into forced engagementof the disc.
 4. The disc brake of claim 2 further comprising movablemeans within the housing engageable with the locking plate meansdiametrically opposite its point of engagement with the associatedmeans; and an axially extending passage through the associated meanspermitting inserTion of a tool to forcibly urge the movable means intoengagement with the locking plate means to cock the locking plate meansout of frictional engagement of the shaft whereby the shaft means,second piston means, and first piston means may be fully retracted intothe housing.
 5. The disc brake of claim 2 wherein the means associatedwith the housing comprises; a rotatable member received through the wallof the housing and having circumferentially spaced axially extendinggrooves formed on the periphery of the portion thereof within thehousing; sleeve means within the housing having circumferentially spacedaxially extending grooves formed on the peripheral portion thereofsurrounding the grooved portion of the rotatable member and having onthe outer periphery thereof a helical groove; a helical groove formed onthe housing and mating the helical groove of the sleeve; bearing ballslocated in the respective grooves whereby upon rotation of the rotatablemember the bearing balls impart rotary and consequent axial movement tothe sleeve.